This invention generally relates to an alkaline cell comprising manganese dioxide. More particularly, this invention is concerned with an alkaline electrochemical cell that is capable of providing optimum service at various discharge conditions.
Commercially available cylindrical alkaline electrochemical cells are widely available in cell sizes commonly known as LR6 (AA), LR03 (AAA), LR14 (C) and LR 20 (D). In many cases the cells are purchased by consumers and then stored until they are needed to power a device. Due to the proliferation of battery powered devices, many consumers own numerous battery powered devices. Some of the devices that may be found in one home include: a radio; a remote control for a television set; a tape recorder; toys for children; an handheld electronic game; a compact disc player; a camera that incorporates a flashlight unit and 35 millimeter film; and a digital camera. Collectively, these devices represent a wide range of electrical discharge conditions. For example, a tape player is known within the battery manufacturing field as a “low drain” device because it needs the battery to supply current at a low rate and with substantial rest periods between activations. A typical discharge regime for a battery in a tape player can be simulated by discharging a single LR6 size battery at 100 milliamps for one hour per day. Another device, such as a flashlight powered by LR6 size batteries, imposes a low to moderate drain on the battery. Discharging an LR6 battery across a 3.3 ohm resistor for four minutes per hour, eight hours per day, is an accepted test for simulating LR6 performance in a flashlight. Yet another device, such as a compact disc player, requires several batteries to supply current at a faster rate than is required by a tape player but with substantial rest periods between activations (i.e. 250 milliamps for one hour per day) and is known as a “high tech” device. Other devices, such as cameras with 35 mm film and a flash unit contained therein, require the battery to supply current at a substantial current (i.e. 1000 milliamps, 10 seconds on, 50 seconds off, for one hour per day) and is recognized as a “high drain” device. When consumers purchase batteries, the consumer may not know the device into which a particular battery will be inserted. Consequently, the consumer will attempt to purchase batteries that perform well in a variety of devices that may impose low drain, or high drain or high tech discharge conditions. If a consumer believes that a particular brand of battery provides optimum service when used in all devices, then the consumer will be motivated to buy that brand of batteries rather than a different brand of batteries. Consequently, many battery manufacturers strive to develop and market batteries that are perceived by the consumer as “all purpose” batteries because the batteries power a wide range of devices for acceptable periods of time.
In addition to improving the length of time that their products will power a variety of devices, battery manufacturers constantly strive to reduce the cost of the battery. One way to reduce the cost is to decrease the quantity of electrochemically active material in one or both of the battery's electrodes. For example, the quantity of zinc in the anode and/or the quantity of manganese dioxide in the cathode could be reduced. However, this option is not acceptable to the manufacturer because any reduction in the quantity of electrochemically active material usually decreases the battery's “run time” which is the length of time the battery will run a device.
Previous attempts to address the problem of how to improve a battery's performance in a particular device, such as a camera, have usually involved changes to the cell's internal construction. In one example, the cell construction was modified by increasing the quantity of zinc in the anode. However, this change resulted in unacceptable leakage of electrolyte after the cell had been deeply discharged. In another example, instead of using a cell design in which one electrode is inserted into a centrally aligned cavity defined by the other electrode, some manufacturers have used a “jellyroll” construction in which two strip shaped electrodes and one separator are aligned with one another and then rolled to form a coil. Batteries with jellyroll constructions typically perform well in high drain devices. Unfortunately, the same cells provide substantially reduced service in low drain devices because a substantial portion of the electrochemically active material must be replaced with chemically inert separator due to the jellyroll's large anode-to-cathode surface area. Consequently, batteries made with a jellyroll construction are not well suited for use in devices where the cell's total electrochemical capacity is more important than the ability to discharge at a rapid rate.
Therefore, there is a need for an inexpensive alkaline electrochemical cell that has the ability to provide adequate run times in devices that require the battery to discharge at a high tech drain rate as well as provide adequate run times in devices that require the battery to discharge at a low drain rate.